Methyl methacrylate-based materials which have hitherto been widely used as a denture base resin, a crown and bridge resin, or a filling resin have excellent advantages in operability, esthetics, stability in the oral conditions, etc. On the other hand, since these materials are poor in mechanical strengths, they have drawbacks in terms of strength such that, for example, in the preparation of a denture, after polymerization in a gypsum mold by the usual manner, it is broken when dug out from a flask, the denture is broken when dropped inadvertently, and that in the case that the denture is set in the mouth, it is broken when biting.
Taking into account the temperature feeling, sense of taste and extraneous feeling when set, it is desirable that the denture is as thin as possible. However it is actually impossible to render it thin from the standpoint of its strength. Further, when used as the crown and bridge resin, because of its poor abrasion resistance, there is a fear that the labial surface have wear off by brushing, etc. or the incisal edge thereof is broken.
In order to remove these drawbacks, some attempts to improve the mechanical strengths from the viewpoint of formulation have been made. For example, in denture base materials of a powder-liquid type, a method for adding as a crosslinking agent an aliphatic, di- to tetrafunctional methacrylic acid ester-based monomer to the formulation solution is generally employed. The addition of such a crosslinking agent improves the hardness and abrasion resistance to a some extent, but it renders the material brittle to thereby reduce the bending strength. Further, if a large quantity of the crosslinking agent is added, not only the adhesion to the resin tooth is reduced, but also the denture which has been highly crosslinked after the polymerization cannot be repaired by a cold-curing resin. As the powdery polymer, those which are intended to be improved in the physical properties by incorporating a copolymer of methyl methacrylate and vinyl chloride or styrene are commercially available, but they are not always expected to be greatly improved in the hardness and bending strength. Still further, as the liquid component of the crown and bridge resin, difunctional or higher functional methacrylic acid ester-based monomers are in general widely used. In this case, the abrasion resistance upon which the crown and bridge resin using methyl methacrylate is poor is improved, but the toughness and bending strength become lowered to cause a breakage of the incisal edge.